Shortest Path Bridging (SPB) is an emerging standard that specifies methods to overcome traditional inefficiencies in Ethernet based networks by using shortest path based forwarding for unicast and multicast traffic. For multicast, SPB specifies a mechanism referred to as source/group tree that requires building a multicast tree per source node and per Equal cost tree algorithm. This has two main issues; namely, the consumption of computing resources, and the consumption of multicast addresses or other data resources such as shortest path Virtual Local Area Network (VLAN) identifiers. In particular, the computational resources consumed at each node correspond to the number of nodes in the network. Further, the multicast forwarding or filter entries consumed at each node is proportional to the number of nodes in the network that the respective node must send or transit traffic towards.
IEEE Draft Standard P802.1aq, entitled Local and Metropolitan Area Networks-Virtual Bridged Local Area Networks-Shortest Path Bridging specifies shortest path bridging of unicast and multicast frames, including protocols to calculate multiple active topologies that can share learnt station information, and support of a VLAN by multiple, per topology VLAN identifiers (VIDs). IEEE Draft Standard P802.1aq is incorporated herein by reference in its entirety.
There are several techniques known for reducing overhead of source specific trees for each service instance (I-SID). According to one technique, head end replications are used with unicast paths. Unfortunately, this technique wastes bandwidth throughout the network. According to another technique, grouping is used to reduce the number of service specific addresses. Unfortunately, this technique is inefficient and uses a high number of trees.